Busy-test system.



Pat-annu upf. 2a, V1902.

BUSY TEST ISYSTEM,

(Application med pn s. 1902.)

(No Model.)

zo tions of the same circuit.

y UNITED4 STATES,

PATENI"N FFICE..

DAVID S. HULEISH, `OE CHICAGO, ILLINOIS, ASSICNCR To THE AMERICAN BELL TELEPHONE COMPANY, or BOSTON, MASSACHUSETTS, A CORPORA- TION CE y MASSACHUSETTS.

vinueva-yTEST SYSTEM,

,y SPECIFICATION arming part f Letters Patent No. 712,455, dated eczeem- 2e, 1902. Original application led November 5,1901,.Se`rial No. 81,252. Divided and this application iiled April 5,1902. Serial i f i N0.101.504. `(No model.)`

To ctZZ whom, it may concern:

`Be it known that I,"D'AVID S. HULFISH, re` siding at Chicago, in the county of Cook and State of Illinois, have invented Certain Im` provements in Busy-Test Systems and Apparatus, of whichthe followingisa specification. 4

Tlie in Veniion relates particularly to busytest systems foruse in conjunction with polyro station Subscribers circuits of central-battery telephone-exchange systems `and apparatus, the object being to provide abusy-test system which can be applied for any circuit `to the switchboard by means of the switch *.5 devices when the desired connection involves the switchngof the circuit lrofanother line or independent of said switching devices and central-station manipulation whenthe cornmunication established is between two starlhis application is a division of my appli` cation filed November 5, 1901, Serial NO. 81,252, the prescntinvention being herein described `and illustrated as applied to the cenz 5 tral-battery telephone-exchange system and apparatus constituting the subjectmatter claimed in said original application.

` In accordance with my present invention I arrange a relay in `the main metallic circuit 3o which when said metallic circuit is closed by the displacement of a receiverat any substation acts to connect the test-pieces of the several switch-sockets with a source of testing poten-tial, and I also provide means for attaining the same end when theline in question is switched at any of its switch-sockets.

I thus protect thel said main circuitwhen,` l

indicate that the switchboard C is or may be `a multiple switchboard. 9o

already in use from interruption under all circumstances. Moreover, in lthe first case` 4o the busy test is set without operating the cutcircuit 2S,extendin,e,r to earth or return through olif relay to disconnect the normal circuit connections; but in the latter case itis arranged that the application of the testing current shall operate the said cut-Cif relay.

The drawing accompanying and illustrating this specification is a diagram of a polystation or party line or circuit extending from a central station toa plurality of substations.

Iwill rst describe the arrangement of cir- 5o cuits with which my busy-test system is associated, as illustrated in the drawing.

ycalls, and r r2 are resistance devices.

L is the metallic line-circuit, and a. b represent its main conductors, respectively. It

is connected with the switchboard C at the central station O and extends outwardly therefrom to the substations S, S2, and S3.

At the central station I-I is the central source of current, connected between the mains a. b ofthe circuit and having aground connection at one of its poles 36.' 6o

Gis the usual im pedance-coil, having windings m n in the two main conductors, respeci `F is a differential relay or electromagnetic Switch having its two coil-windings g and h in the said two main conductors; but the said coils are wound or connected to oppose one another-.when a current from the source H flows in the metallic circuit Il. The said electromagnetic switch is therefore irresponsive 7o or null to such a current. Obviously, however, a similar' current iiowing` through one only Of its windings will magnetically excite the appliance, which thereupon will operate to attract its armatures. Under the conditions of this specification the coil g is the one which alone acts to excite the core. I

R is the cut-olf relay; D, a relay controlling the application Cf the busy-test potential to the test rings or points cl of the switch-sockets J J2 whenthe circuit is engaged by communication between two of its own stations.

M is the independent or call generator, usually7 a magneto-electric lalternating-current generator.` 85

`N is a signal device to indicate incoming Theswtch sockets or jacks J JL sufficiently The signal device N is con nected in a branch the armature and iixed contacts 27 26 of the `switch-relay F from point 34 of conductor 24.

This branch circuit, and therefore the said sig- I nal N included therein, are controlledbythe maintaining the normal connection of the main conductor b. The normal connection of main conductor d as it enters the central lstation and after passing its switch-socket` branches isthrough -contact-pieces e and 2l of the eut-off relay, winding of relay D, coil g of differential relay F, coil m of the impedancecoil, and conductor 22 to the source H at its ungrounded pole 23, while that of conductor b is by way of the cut-ol-relay contacts fand 37, conductor 3S, movable and xed contact-points 39 and 40 of the differential relay F, coil h of said relay, winding 'n of the impedance-coil G and conductor 41 to the grounded pole of the source H at 3G. The call-generator connection is thus controlled bythe differential relay F, and when the latter becomes lexcited and the armature-contact 39 transferred from the back stop 40 to the front stop 4t2 the normal connection of the main conductor Z) with the source H including the coil h is broken and the call-current generator M is united to the said main conductor in place thereof.

The apparatus at all of the substations is alike; At each is the usual electromagnetic call-bell B and the condenser c in a bridge 7 together between points 12 13 of the main conductors a and b, respectively, and the said bridge also, as usual, is held conductively open but inductively closed for the passage of the rapidly-changing call-currents by means of the said condenser.

T is the telephone-transmitter; t, the receiver, I, the transmitter induction-coil with its primary winding t and secondary winding ft2, and s the suspension-switch, serving as a support for the receiver when the station apparatus is not in use and controlling the continuity of the telephone-bridge o and local circuit. The said telephone-bridge t* is shown as extending between the same points 12 13 of the main circuit-conductors and as leading through the transmitter T and the secondary winding i2 of the induction-coil. It is open normally or While the switch s is held depressed by the weight of the receiver in said switch at the point 3. The said switch also controls the local circuit, which includes the receiver t and the primary coil t' and which may be regarded as looping from point 6 to point 8 of the bridge 7, so that it includes the condenser c. The transmitter T, besides being in the telephone-bridge, is in this local circuit also.

Two grounding-keys c k2 are attached to the two main conductors ct and b, respectively, at the points 14 l5 in each substation. The said keys have front contact-anvils 19 and 20, bolh connected to earth at E2. Normally they produce no effect on the circuit; but when either key is depressed it grounds its own main conductor directly. Moreover, when key lc is depressed it not only connects its own main conductor a, directly to earth, but also connects the other main conductor b to earth through the inductivelyclosed bridges 7 of their respective bells B. So,a1so, key k2 when depressed grounds the main conductor b directly and also grounds the other main conductor a. through the telephonebridge of any substation or substations where such telephone-bridge is closed by the displacement of the receiver from the suspension-switch. v

' I will now describe in detail the busy-test system as applied to the above-described arrangement of substation-circuits.

Referring again to the central-station appliances, it will be seen that abusy-test conductor 31 unites the several switch-socket test-frames d and a connection 24: from the source H or any similar source of testing potential extends to said test-frames through the contacts 29 l30 of the special relay D and a resistance r. The magnet-ooil of the cut-oit relay R is in an earth branch 33 from testconductor 3l at point 32. When two substations of the same circuit are talking together, it-is quite as necessary to protect the circuit from interruption as it is when the line is switched for communication between one of its own stations and a station of another line; but under such conditions it is required that the cut-off relay shall not be operated. This is accomplished by the use of relay D. When two stations of the same circuit are in communication, their receivers are taken from their suspension-switches and the metallic circuit is completed, so that the current of l battery H can flow therein through the magnet-coil of relay D. The said relay is thus excited and the contact 29 30 is made, establishing an electrical testing potential upon testrings d by connecting them through conductors 31 and 24 with the source H at pole 23. The resistance fr is of such magnitude that with a normal adjustment of the cut-o relay R any current passing through the'said Y relay R is insuflicient for its operation.

vHence the busy test employed during the communication between two stations of the same circuit can be applied without operating the cut-off relay, and therefore without interfering with the circuit connection between the main circuit L and the source H, whose current is required for the supply of the substation-transmitters.

P is the answeringplug of an ordinary switch-cord, (not shown,) and, as usual, its local or sleeve contact surface 103 registers with the test-ring d of any socket wherein it isinserted. Thesaidsleeve-contactis united by the local cord conductor 50 and its eXtension 5l to the battery H2 and ground. Thus Whenever the said plug is inserted in a socket d to answer or make a call the current from battery H2 flows over the local circuit thereby established to operate the cut-off relayR in` such local circuit and to impress a test potential upon all other switch socket testpieces belonging to the samesubscribers circuit.

It is now evident that when the line is en- IIC `gagedin a local communication between two y of its own substations the busy-test poten-` tial is impressed upon its test-rings through,` the intermediation ot' tlie eXtra relay `D and t that during the engagement of said line by; switchingit `to another line'forcommunicm` tionbetween stations of` the said `two lines the busy-test potential is impressed upon the test-rings by Wayot` the thirdor -local plug-V contact, the conductor thereot`,and thebat#` teryconnectedtherewith. Inthe formercase,

` it is necessary to retain the `normal connec` tion oftthesource H, and accordingly'means are provided to prevent the operation `of ther: cut-od relay R; but; in the latter case it ism desirable to disconnect said battery H, and

the, cut-od relayis` made to operate In either case should the line protected lie-Ide,

test-potential impressed upon said rings is"` `manifested as a sound in the receiver, which otherwise is silent.` y t In the general operationv of the signaling4 devices of the systemtlet itbe assumed thattheir bells.

a person at `any substation, as S2, `vishes to communicate withV another station of the samecircuit-forinstan`ce,S. He first takes up the receiver from the suspension-switch s and `listens to ascertain'whether or not the line is already employed by some other vstation. Finding thecircuit free 'he returns the receiver toithe switch-hook and then to opV -erate the bell at station S presses the grounding-key 711. Vrl`hisresults in the ringing of the bell at all the substations; but as each has its own code-signal and as the key is operated in a manner to correspond with station S onlyA all other stations will disregard the ringing of When the said key is operated, a ground-circuit is closed over main conductor a between the ground connection at pole 36 of battery H and the key ground connection at substation S2. This is traceable from pole 23 of said source by conductor 22, impedancecoil fm, the coil g ot the differential electromagnetic sWitch F, relayD, contacts 2landA e of cut-olf relay R, main conductor ct, point 14 on said conductor at substation S2, branch 17, key Zt, contact -anvil 19, conductor 1S, and ground E2. There being no current through the other coil h of the electromagnetic switch F, that in the coil g is effective and the said switch is operated and attracting itsarmature39 breaksthe normal circuitof conductor and unites the said conductor, of which said armature is the terminal, to the source M of call-current, of which front stop 4t2 isthe terminaL The current of said call-generator` .then passes over the grounded circuitof main conductor b, `which circuit extends from the `ground ot'. the key `k at substation S2 by way l,of` generator` M, conductor `43, resistance r2,

contacts 42 fandBf) ot' the relaylswitch F,con;

"ductor 3S, contacts andfofthe cut-off re- ,lay R, main conductor b, and-reaching the severalsu bst ations through their ind uctively` closed bell branches 7 in parallel4 to main con-` duct-orc, and thus to the key k, the ringingcurrent dividingbetween said t bell branches The operation of the relay-switch F includes ground conncction'of said `generator to the) fthe attraction of itsarmature 27, which closes i the circuit 2Sot the lamp-signalNpbut as y :the code-,signals are. distinctive and quite dif- "ferent from the central -station signalthe 1 flashings of said lam p-signal,which when such sieut and fluctuating, will be ignored by the operator, who on observing such brief flash- `ings readily understands that one substation `is calling another.- A

lstation'wanted, the `person who has called` `Havingr obtained a response from the subfrom S2 ceasesto operate key 7c and again 11e-1 f moving the receivertfrom switch s begins the 1 conversation. d

lcircuit tests busy'dagainst alltcomers, because tors 24 and 31 and resistance if. y

At the saine time `the `main the relay D by operating .hastconnected the test-rings d with a battery through conduc- 'lhe` battery H is retained inrconnection `bode-signals are being transmitted are tranlo.: i

1 with the circuit'to su pply transmitter-curren t, i

because the cutott relay has not operated,

the current through resistancer beinginsuf= ficient for itsoperation, and since currenty now flows through the neutralizing-,coil 7L also of the relay-switch Ethe said switch has become null, disconnectingithe call-generator and causing the liashes `of signal Nto cease.

Let it nonT be assumed that a substation-` say S-desires to obtain a connection thron gh -the switchboard with a substation of another circuit. The receiver' t is to be removed from the switch s, as in the formercase, so that the person desiring to use the line may tindout whether it is disengaged' but in this case `nding the circuit free, the receiver is notre-` placed, but remains oit the hookuntil the close ot the communication; The key k2 is` now to be steadily depressed, no code-signal being required in the transmission of a central-station signal. The line-conductor a, as in the former case, constitutes a `grounded circuit for the current ofsource H, the route of such circuitat the. central station being the same as before, but at the substation being from main conductora through the closed telephone-bridge 7 to-key` 7a2 and `ground .by Way of point 12, conductor 2, transmitter T, suspension-switch s, point 3secondary induction-coil winding 712, conductor lu, points 13 and `15 on `main conductor b, branchlp key k2, contact-anvil 20, and connection 18.

IIS

their several functions.

and the exciting-coil .g only of relay F, these l relays both become operative and perform Armature 27 of the latter is n'ow steadily attracted, maintaining the branch circuit 28 of signal N steadily closed and the said signal steadily displaced until the call is answered. The substationbells are not r-ung, because although the armature 89 of the relay-switch F is attracted and the call-generator thereby united to conductor h the currents of` said generatorv are shunted from the bells by the resistanceless ground applied to conductor l) at the key k2 of the calling substation. The resistance r2 is ot' such magnitude as to prevent the call-v currents from f attaining an undesirable strength while thus substantially short-cirn cuite'd. When the call is answered by inserting the answering-plug P in the socket J2 of the calling line, the busy-test potential is impressed upon the test-rings of the multiple switch-sockets in the regular way through the third or local plug and cord conductor, and since current can now flow through said cord conductor to the cut-off relay R by way of a path independent of the resistance r the said relay is operated in a manner and for a purpose well understood.

The use of the impedance-coil G is in part to regulate the current admitted to the line and partly to prevent waste or diversion of the voice-currents when two stations of the same circuit are conversing.

When the main circuit L has been switched to another circuit at the central station and the cut-off relay has been operated, as described above, the impedance-coil G, relayswitch F, and test-current relay D are severed from the said circuit and of course cease to exercise their several functions.

From what'has been stated it is evident that no call-signal can be transmitted simply by removing the receiver from the switch, but that such action alone merely sets the automatic busy test; also, that to call other substations of the same circuit one key must be operated in correspondence with the codesignal of such stations, the receiver being in place on the switch, and that to call the ceutral station from any substation the other key must be steadily depressed, the receiver being kept o the switch. I

It is to be understood that while for clearness two sources H H2 of steady current are shown and described a single source is in practice preferably employed and also that such single source in practice may be common to a number of main circuits.

Having thus described my invention, its nature and operation, I claiml. In a busy-test system for central-battery telephone-exchanges, the combination with a plystation-circuit system comprising a metallic main telephone-circuit extending be- 'tween a centralstation and a plurality of substations; a battery or like source of current in said metallic circuit at the central station; a call-bell in a conductively-open bridge of said circuit, telephone instruments in an independent normally open bridge of said circuit, and a suspension-switch operated by the removal of the receiver therefrom to close the circuit through said telephone-bridge, all at each substation; aud a battery or like source ofcurrent in said metallic circuit, a call-receiving signal device -in va local circuitof said battery, a differentially-wound relay in said main circuit controlling said signal device and held by its opposing coils irresponsive to the operation of said suspension-switch, and a multiple switchboard with which the said main circuit is connected, of a single-wound relay in said main circuit responsive to said suspension-switch, and a branch circuit leading from said battery through the local contact-points of said last-named relay to the busy-test pieces ot' the several switch-sockets .of said main circuit on said switchboard, all

at said central station, substantially as set forth.

2. In a busy-test system for central-battery telephone-exchanges, the combination with a metallic main circuit extending between a central station and a number of substations; a battery at said central station connected between the main conductors of said main circuit; a plurality of switch-sockets at said central station with which said circuit is associated; switch-plugs coperating with said sockets; a busy-test circuit-conductor uniting the test rings or points of the several switch-sockets of said circuit; a cut-off relay in a branch or extension of said conductor; means-associated with said switch-plugs for establishing a busy-test connection between said switch-socket test-rings and the said battery or like source of testing-current when the said main circuitis switched; and aswitch at each substation to close said main circuit throughthe telephones of said station; of an independent and normally discontinuous electrical connection between said source of testing-current and said busy-test conductor; a relay in the main circuit responsive to said substation-switch controlling the said connection and adapted when excited to establish the same; and means as indicated for permitting the operation of the cut-off relay by the current of the testing-potential when applied through the switch devices, and for preventing such operation when the said current is applied by said relay, substantially as described.

In testimony whereof I have signed my name to this specification, in the presence of two subscribing Witnesses, this 28th day of March, 1902.

s DAVID S. HULFISH. Witnesses:

S. G. MGMEEN, H. W. CAsLow.

IOC

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